public function rules() {
    return [
        "username" => "required|min:3|unique:users",
        "password" => "required|min:6|confirmed",
        "email" => "required|confirmed|email|unique:users",
    ];
}

public function postRegistration(RegistrationRequest $request) {
    $this->user->username = $request->input('username');
    $this->user->mail = $request->input('email');
    $this->user->password = password_hash($request->input('password'), PASSWORD_DEFAULT);
    $this->user->save();

    $this->auth->login($this->user);
    return redirect('/dashboard');
}